Gray "T" handle/control replacement

[Tafakot]

Hi, hello and I'm having a great day.
My "Q" is on replacement or repairing the "T" cable/valve for my Gray tank.
It has gotten "spongey" and doesn't seem to want to close all the way.
I'm a fulltimer and have open and closed both black/Gray a gazillion times and I've flushed both fairly well and pretty often.
Other RVers have suggested theres most likely particulates in the blade grove preventing it from complete closure or...the cable has stretched.
Either way, I'm going to have to open The Belly of the Beast and trace the cable and/or replace it or the mechanism itself.
Not being able to receive blueprints/schematic or even a cartoon drawing from Keystone in order to remedy the issue, I would appreciate some professional (or semi-professional) knowledge on the best way to go about this.
Also, I've been told..."cut the belly pan and tape it up when done" which doesn't play well in my mind.
Having been under the rig numerous times, the thought of dropping the pan is slightly this side of a nightmare.
Ok people...1...2..l3...GO